Touchscreens are widely used as input means on displays of smart devices such as personal digital assistants (PDAs), laptop computers, smartphones, and tablet computers, as well as other electronic devices such as office automation equipment, medical equipment, and car navigation systems.
There are various touchscreens that utilize different position detection methods, such as optical, ultrasonic, surface capacitive, projected capacitive, and resistive, touchscreens. Resistive touchscreens include an optically transparent conductive material and a glass plate with an optically transparent conductive layer, which face each other with a spacer therebetween. An electrical current is applied to the optically transparent conductive material, and the voltage of the glass plate with an optically transparent conductive layer is measured. In contrast, capacitive touchscreens basically include an optically transparent support and an optically transparent conductive layer thereon and do not include movable parts. The capacitive touchscreens have high durability and high optical transmittance, and are thus used in various applications. Projected capacitive touchscreens are also capable of simultaneous multipoint detection, and are thus widely used in devices such as smartphones and tablet PCs.
Conventional transparent electrodes (optically transparent conductive materials) for touchscreens usually include an ITO (indium-tin oxide) conductive film as an optically transparent conductive layer formed on an optically transparent support. Yet, ITO conductive films have a high refractive index and high surface reflectivity, so that optically transparent conductive materials including an ITO conductive film unfortunately have a reduced total light transmittance. In addition, due to low flexibility, such ITO conductive films are prone to crack when bent, resulting in an increased electrical resistance.
As an alternative optically transparent conductive material including an optically transparent conductive layer different from an ITO conductive film, Patent Literature 1 and Patent Literature 2, for example, each disclose an optically transparent conductive material having a metal thin wire net-like pattern on an optically transparent support, which can be obtained by a method (semi-additive method) in which a thin catalytic layer is formed on a optically transparent support, a pattern is formed thereon using a resist, a metal layer is stacked on resist opening portions by plating, and lastly, the resist layer and a underlayer metal protected by the resist layer are removed.
Recent proposals also include a method that uses a silver halide photosensitive material produced by a silver salt diffusion transfer process as a conductive-material precursor to produce a metal thin wire net-like pattern. For example, Patent Literature 3, Patent Literature 4, and Patent Literature 5 each disclose a technique for forming a metal (silver) thin wire pattern by reacting a conductive-material precursor with a soluble silver halide forming agent and a reducing agent in an alkaline fluid, wherein the conductive-material precursor includes at least a physical development nucleus layer and a silver halide emulsion layer formed in this order on an optically transparent support. A metal thin wire pattern produced by this method can reproduce uniform wire width, and can also provide high conductivity with a narrower wire width compared to patterns produced by other methods because silver has the highest conductivity of all metals. The optically transparent conductive layer obtained by this method is also advantageous in that it has higher flexibility and higher bending resistance than ITO conductive films.
Projected capacitive touchscreens include a touch sensor formed of an optically transparent conductive material on which multiple sensor parts are patterned on the same plane. If such a touch sensor is formed of an optically transparent conductive material only having multiple sensor parts, the sensor parts will be noticeable. Thus, usually, dummy parts that are non-conductive with the sensor parts are arranged at portions where the sensor parts are not patterned on the optically transparent conductive material. For example, Patent Literature 6 suggests a method for disposing sensor parts and dummy parts by dividing a metal thin wire pattern by slits. Patent Literature 7 discloses an optically transparent conductive material in which disconnection parts are provided within a metal thin wire pattern to cut off conduction from sensor parts so as to form dummy parts and in which the difference in aperture ratio between the sensor parts and the dummy parts is specified. Patent Literature 8 suggests a method in which a metal thin wire net-like pattern of sensor parts and a metal thin wire net-like pattern of dummy parts are shifted along the boundary between each sensor part and each dummy part so as to cut off conduction of the dummy parts from the sensor parts. Patent Literature 9 discloses dummy parts formed in a metal thin wire net-like pattern formed by an assembly of multiple polygons each including a disconnection part. Patent Literature 10 suggests a method for providing floating electrodes (dummy parts) separated from sensor parts via disconnection parts.